PROJECT SUMMARY ? ABSTRACT The Childhood Leukemia International Consortium (CLIC), established in 2007, is a group of independent, international researchers who study the role of environmental, genetic, infectious, and clinical risk factors in the etiology of childhood leukemia through the sharing of data from case-control, family-based, and registry linkage studies. Over the past 3 years, CLIC investigators have begun to expand these collaborations to other childhood cancer; an effort dubbed CLIC+. CLIC/CLIC+ now includes 50 childhood cancer case-control studies worldwide from 19 countries (39 PIs) representing approximately 43,000 leukemia, 14,000 CBT, and 18,000 embryonal tumor cases and 3.9M controls. Most of the studies have comprehensive epidemiologic data, and about half have biospecimens. Though CLIC/CLIC+ members participate in teleconferences throughout the year, the annual in-person meeting for members is essential for planning and evaluating progress on collaborative research projects, and discussing new research directions. The 2019 CLIC annual meeting will provide a forum for continuing discussions and increasing the knowledge base of members. It will also achieve the following goals: Plan and conduct pooled and validation studies on the environmental and genetic risk factors (including GxE interactions) for childhood leukemia, brain tumors, and embryonal tumors. Present and discuss plans for continued expansion of CLIC+ intiative to include other childhood cancers, especially brain tumors, which will take advantage of our existing infrastructure, collegial relationships, and knowledge; evaluate current literature to identify gaps in research where CLIC can best contribute. Identify and address methodological challenges, e.g., the impact of possible selection and recall bias, application of statistical methods for causal inference, meta-analysis of GWA data. Partner with leading national institutes of health to identify potential studies of under-represented children with cancers; continue to encourage participation and increase membership of under-represented populations from Central and South America and Asia. Provide an avenue for exceptional professional development to junior investigators to maximize their potential for success. Discuss and identify research areas most suitable for quantitative research translation, research dissemination and communication to stakeholders.